GB762902A - Forced flow, once-through, tubulous vapour generators and methods of operation thereof - Google Patents

Abstract

762,902. Combustion apparatus. BABCOCK & WILCOX, Ltd. June 24, 1954 [June 26, 1953], No. 18522/54. Class 51 (1). [Also in Group XIII] A forced flow, once-through steam &c. boiler, especially for operation at super-critical pressures, comprises three independently operable cyclone furnaces 10, of the form described in Specification 552,747, arranged to discharge high temperature gases into a secondary furnace 11 whence the gases flow through a slag screen 12 into a vertical radiation and gasmixing chamber 13 and discharge therefrom through a lateral pass 14 in which is disposed a secondary superheater 16, the rear portion of pass 14 being divided into parallel passes 14a, 14b locating respectively a convection primary superheater 17 and high and low pressure reheaters 18, 19, the gas flow through each pass being controlled by dampers 130, 131. From passes 14a, 14b the gases flow into a common outlet duct 20 leading to an air heater 21 and an induced draft fan 22. Combustion air is supplied to the furnaces by a fan 24 which delivers the air through duct 25, the air heater and ducts 28. A regulated portion of the cooled flue gases is withdrawn from duct 20 through a conduit 29 leading to a fan 30 from which it passes through duct 31 and ports 122, 124 into chamber 13 at sufficient velocity to ensure intimate mixing with the fresh gas and in sufficient quantity to ensure that the temperature of the mixed gases at the entrance to pass 14 is such that entrained slag particles are in a solidified condition and that overheating of superheater 16 is avoided. Feed water at a pressure, for example, of 5500 pounds per sq. in., is supplied to the inlet header of the cooling tubes of one of the end cyclone furnaces and passes successively through these cooling tubes and those of the other two furnaces to an outlet header whence the heated water is conveyed to the inlet header 68 of the primary superheater 17, the furnace heating surfaces being so arranged that the transition zone occurs in this superheater. Steam from the superheater 17 passes via headers 69, 70 into a radiant superheater consisting of serially connected tube panels lining the walls of chamber 13, the final superheating of the steam being effected in the secondary superheater 16. The final steam temperature is controlled primarily by controlling the firing rate of the cyclone furnaces 10, further control suitable for operation at partial loads to raise the steam temperature being provided by varying the number of furnaces in use and by regulating the quantity of recirculated gas. Specifications 201,304, [Class 51 (i), 206,559, [Class 122 (iii)], 398,413, [Group XIII], and 762,940 also are referred to.